PVR systems offer consumers a hard disk-based VCR-like function that records live TV programs, while offering the versatility of select playback and associated special features. One feature of a PVR system is to provide the consumer with the ability to pause viewing of a live broadcast for a variable length of time while the unit continues to record, and then resume continuous viewing from the point of departure. This feature is typically referred to as time-shifting. Since the programs are recorded digitally, the viewer may also take advantage of trick mode features such as pause, fast forward, slow forward, rewind, slow reverse, skip, and the like.
PVR systems have been gaining popularity with television viewers. Examples of currently available PVR systems include the TiVO system available from Philips Electronics and Sony and the Replay system available from Panasonic. PVR systems from other manufacturers are available as well.
PVR systems typically receive and decode analog video from broadcast sources, compress the decoded video and audio into a digital format such as MPEG, and record the compressed data onto a hard drive. For playback, present systems read and decode the compressed digital video and audio from the hard drive and output the decoded video and audio in an analog format for display.
Using trick mode features such as fast forward and reverse display functions, the viewer may reach a desired point in the broadcast by viewing the video pictures faster than the normal display speed and/or by viewing them in reverse. It is desirable that the PVR systems present the pictures during fast forward and reverse displays with a quality sufficient to allow the viewer to readily locate the desired point in the broadcast. Fast forward display and reverse display may also be referred to as cue and review, respectively.
Present PVR systems typically perform the function of encoding the video into a digital format that allows for cueing and reviewing during playback of the stored contents. However, in digital cable systems, for example, the video is encoded in a digital format before it ever reaches the PVR system. Such a format may not be conducive to enabling cue and review with adequate picture quality when the digitally encoded streams do not have a substantial number of I-pictures, which may include the case of having no I-pictures altogether.
For example, performing trick modes with no-I-picture digitally encoded streams, such as General Instrument/Motorola's progressive refresh streams or streams provided by AT&T's Headend in the Sky (HITS) service, is generally more difficult than with MPEG video using a conventional IBP GOP structure. This is because in progressive refresh streams or HITS streams there are no I-pictures to which the decoder can perform random access.
Therefore, it is desirable to provide a method and apparatus for enabling trick modes when the digitally encoded streams do not have a substantial number of I-pictures.